This invention relates to a weft detaining device for detaining a predetermined length of a weft yarn from weft yarn supply means, prior to weft picking by weft inserting means.
In connection with a shuttleless loom, a spun yarn which is relatively small in tensile strength has come into use particularly in air jet type shuttleless looms. Accordingly, it is desirable to control the weft yarn tension, since a slight variation in tension can break the weft yarn. Conventional devices detain the weft yarn in lengths of about 2/3 of that required for each weft picking. The weft yarn tension abruptly increases when the yarn is changed from its free flight period, in which the detained weft yarn is picked, to the measuring flight period in which the weft picking continues measuring the length of the weft yarn. Therefore, it is necessary to detain the weft yarn in a length of one weft pick in order to draw the weft yarn from the detaining device with little resistance. This is achieved by a device disclosed in Japanese Patent Publication No. 51-34499. In this device, a ring having an annular brush is disposed around an end section at the weft inserting nozzle side of a drum having a conical section and a cylindrical section. This drum functions to wind the weft yarn thereon in lengths of one weft picking. The length of detained weft yarn is maintained constant by optically sensing the amount on the drum and rotating the drum accordingly. In this device, the annular brush serves as a stop for the weft yarn at the end section at the weft inserting nozzle side, and functions to prevent the weft yarn wound on the drum from coming off.
With such a device, since more weft yarn than that required for one weft picking remains on the drum, the weft picking is accomplished with the weft yarn which is completely detained on the drum and therefore an abrupt variation in weft yarn tension does not occur during weft picking. However, the weft yarn always receives resistance to its movement since it is drawn from the drum contacting the annular brush. This results in the following disadvantages, particularly in a shuttleless loom whose weft picking is accomplished by a relatively weak dragging force, for example in the air jet type shuttleless loom: (1) weft yarn shortpicks may occur in the warp yarn shed; (2) higher air pressure is required to overcome the weft yarn dragging force; and (3) the detaining device will not separate the weft yarn in the amount required for one weft picking and accordingly requires a device for restricting the length of the weft yarn to be picked.